@function vw($px) {
    @return $px / 750 * 100+vw;
}

.wrap {
    position: relative;
    overflow: hidden;
    width: 100vw;
    height: 100vh;
    background: url("../images/pic1.png") no-repeat center/cover scroll;
    #back {
        box-sizing: border-box;
        position: absolute;
        padding-top: vw(5);
        top: vw(30);
        left: vw(50);
        width: vw(80);
        height: vw(50);
        background-color: rgba(0, 0, 0, .1);
        text-align: center;
        border-radius: vw(20);
        border: none;
        .icon {
            width: 1em;
            height: 1em;
            vertical-align: -0.15em;
            fill: currentColor;
            overflow: hidden;
            font-size: vw(30);
        }
    }
    .box {
        margin: vw(170) vw(80) 0;
        width: vw(590);
        height: vw(840);
        background-color: rgba(255, 255, 255, .5);
        box-shadow: vw(2) vw(2) vw(3) vw(4) rgba(0, 0, 0, .2);
    }
}